It is regularly necessary to test the insulation properties of components used in hazardous environments such as underground in mines. For instance, the insulation properties of trailing cables which provide power to moving mnachinery must be checked, to ensure that they have not been damaged.
A device has been used for many years for testing insulation in mines. The device contains a voltage generator which generates 500 volts at two terminals which are connected by flying leads to the insulation to be tested. A push button is pressed by the operator to cause the voltage to be generated and a needle meter gives a reading which falls slowly until a pre-determined reading is reached or passed, if the insulation is adequate. If the needle fails to fall, or fails to fall sufficiently, a fault in the insulation is indicated. When the push button is released, the capacitance of the insulation being tested is automatically discharged.
In order to speed up the testing procedure when several items are to be tested, it is common to use this device in an extremely dangerous manner, which does not comply with the requirements of intrinsic safety. (Intrinsic safety is a set of techniques and design criteria which aim to minimize or eliminate the dangers of high voltages in hazardous enviroments.) The push button is held or jammed in its operative position to cause a test voltage to be permanently generated. The flying leads are then connected to each insulation in turn and left in place until a satisfactory reading has been obtained, before being moved to the next insulation. This gives rise to two sources of danger. Firstly, high voltage flying leads are being moved around giving the risks of electric shock, although the voltage source will normally be "intrinsically safe". Secondly, the components which have been tested are not discharged after testing and are therefore left charged to 500 volts. Their large capacitance and the high voltage mean that the charged components are not intrinsically safe, and indeed are extremely dangerous.
It is an object of the present invention to obviate or mitigate these disadvantages of the prior art.